Prospective studies as well as single-point-in-time studies are being conducted in former adult and adolescent drug abusers and alcoholic addicts during methadone maintenance, naltrexone a drug free treatment. Emphasis on the neuroendocrine, hepatic, gastrointestinal and immunological effects of this opioid. Studies are being carried out in stable methadone maintenance patients to determine whether or not liver disease varying types and degree of severity will subsequently alter disposition of methadone in maintenance.